If the prime factorization of the denominator of a fraction has only factors as 2 or 5 or a combination of 2 and 5 then the decimal form of that fractional will be a terminating decimal form.
Consider the fractions 17/20 and 19/6
Now, 20 = 2 x 2 x 5, and 6 = 2 x 3
∴ 17/20 is terminating decimal form while 19/6 is recurring decimal form.